Question: 3 markers cost $3.00. Which equation would help determine the cost of 12 markers?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 3 markers. We want to know the cost of 12 markers. We can write the numbers of markers as a proportion: $\dfrac{3}{12}$ We know 3 markers costs $3.00. We can let $x$ represent the unknown cost of 12 markers. The proportion of these costs can be expressed as: $\dfrac{\$3.00}{x}$ The cost changes along with the number of markers purchased, and so the two proportions are equivalent. $\dfrac{3}{12} = \dfrac{\$3.00}{x}$